This application will test the hypothesis that, in addition to its effects on neurotransmitter production and receptors, estrogen affects gonadotropin secretion in primates by regulating the synaptic connections between elements of the GnRH delivery system. The investigator proposes that by the time of the preovulatory gonadotropin surge, the ratio of the number of stimulatory and inhibitory synapses is higher on GnRH neurons than at any other time during the menstrual cycle. To test this hypothesis, the investigator will determine the synaptic connection and activity of GnRH neurons in the monkey brain during estrogen-regulated control of gonadotropins. During the project period, the investigator will study: 1) experimentally stimulated positive feedback induced by administered estradiol: 2) negative and positive feedback during the normal ovarian cycle; 3) feedback in normal males; 4) effects of ovariectomy with or without hormone replacement; and 5) naturally occurring menopause. Three major inhibitory and three major stimulator neurotransmitter systems will be studied in this project.